To be clear: where's the fallacy of the single cause in what I wrote earlier? It's clear in what you said: you misinterpreted my saying "desirable jobs pay less" as "jobs being desirable is the only cause of the market paying less for some jobs". A cause - from my message, vs the cause - the assumption in your response.
Desirable jobs don't pay less than undesirable jobs. In a capitalist market things are set up so that there is a segment of the population who is desperate for money enough to do jobs that other people don't want regardless of pay. You have offered zero evidence for your original claim nor any supporting arguments that a job being less desirable somehow means it will pay more than a desirable job nor have you defined what makes jobs desirable or undesirable. Does high pay make a job desirable? Maybe to some people. You're applying a blanket statement to a heterogeneous population with nothing to back it up.